SCLK multiplier configuration and utilization

In a standard configuration, the control algorithm executes immediately following each sampling event. The SCLK multiplier modifies this behavior by allowing multiple sampling events to occur within a single control cycle. This note explains how to configure the sampling events and how to retrieve the extra values.

Configuring the SCLK multiplier

When using the ACG SDK, the sampling events are configured from the CONFIG block by setting a SCLK multiplier factor. This spreads equidistant sampling events among the control period, starting from the main interrupt phase.

The Timings tab in Cockpit displays where the ADC sampling events are taking place. This permits to visualize and validate the implemented configuration.

When using the CPP SDK, void Adc_ConfigureSclkMultiplier(int multiplier) must be used in the UserInit(void) function.

tUserSafe UserInit(void) {
  // Sets CLOCK_0 at 50 kHz
  Clock_SetFrequency(CLOCK_0, 50e3);
   
  // Set the SCLK multiplier to 4 (sampling = 200 kHz)
  Adc_ConfigureSclkMultiplier(4);
  
  ConfigureMainInterrupt(UserInterrupt, CLOCK_0, 0.5);
   
  // some other code...
   
  return SAFE;
}Code language: C++ (cpp)

Retrieving multiple ADC samples at once

By default, the ADC block or driver only provides the last sampled value. To retrieve multiple values at once, notably when an SCLK multiplier is used, the ADC history must be used. This can be configured from the ADC block, ticking the “multiple samples per period” option and configuring how many samples are desired. The ADC block then returns a vector containing the values as shown below. The sample with index 1 is the most recent sample.

When using the CPP SDK, Adc_ConfigureHistory must be used in the UserInit(void) to enable the ADC history and configure its depth. Then the Adc_GetHistory can be used in the interrupt routine to get the older ADC values.

tUserSafe UserInit(void) {
  // Sets CLOCK_0 at 50 kHz
  Clock_SetFrequency(CLOCK_0, 50e3);
   
  // Set the SCLK multiplier to 4 (sampling = 200 kHz)
  Adc_ConfigureSclkMultiplier(4);
   
  ConfigureMainInterrupt(UserInterrupt, CLOCK_0, 0.5);
   
  // Setup a history of 4 samples for ADC0
  Adc_ConfigureHistory(ADC0, 4);
   
  // some other code...
   
  return SAFE
}
 
tUserSafe UserInit(void) {
 
  float s0, s1, s2, s3;
   
  s0 = Adc_GetHistory(ADC0, 0); // most recent sample
  s1 = Adc_GetHistory(ADC0, 1);
  s2 = Adc_GetHistory(ADC0, 2);
  s3 = Adc_GetHistory(ADC0, 3);
  
  return SAFE;
}Code language: C++ (cpp)